1. Field of the Invention
The present invention relates to a matrix-type liquid crystal display panel, more particularly, to the driver circuit of the TV picture display unit incorporating a matrix-type liquid crystal display panel provided with a plurality of switching transistors connected to respective picture elements.
2. Description of Prior Art
Conventionally, any matrix-type liquid crystal display panel provided with a plurality of switching transistors connected to each picture element can produce a sharp contrast substantially equivalent to a static driver system even when executing multi-line multiplex driving using a low duty ratio. Thus, the matrix-type liquid crystal display panel normally uses the circuit construction and signal waveforms shown in FIG. 1 (A) and (B). In FIG. 1, reference number 11 indicates a liquid crystal display panel, in which switching transistor 11-c is connected to the respective crossing points of the row electrode 11-a and the column electrode 11-b.
Reference number 11-d indicates the liquid crystal layer between the picture elements and the opposing electrodes. Reference number 12 indicates the row electrode driver substantially comprised of shift registers delivering scan pulses y1 through Yn to each row electrode by operation of the clock pulse .phi.1 to sequentially shift the scan-start pulse P sent from signal control circuit 13. Reference number 14 indicates the column electrode driver substantially comprised of shift-registers, a sample-hold circuit, and a output-buffer circuit which outputs data signals X1 through Xm each having an amplitude corresponding to the shade depth of the display. Column electrode driver 14 samples the data voltages during a specific period when dealing with the picture elements of the corresponding column from a variety of display data delivered in series from data control circuit 15. Column electrode driver 14 then holds the value of the sampled data voltage for a specific period of time before delivering the sampled value to the 1-H (one-scan period) column electrode in sync with clock pulse 01. Data control circuit 15 functions as the video receiver circuit as well as the signal processor circuit for displaying TV pictures. FIG. 2 (A) shows a typical example of a circuit dealing with the Xi-element of the column electrode driver. FIG. 2 (B) shows the typical waveforms generated by this circuit, in which control signals T and CL are respectively delivered to all columns. Reference numbers 21 through 24 indicate the respective analog switches that are activated when the control signals Si, T, and CL are High. First, when control signal Si is High, analog switch 21 is activated only during the 1-H period. The voltage of the display data D is then sampled by capacitor 25 during this period, followed by the execution of sequential sampling of the voltages from all the columns.
After completing the sampling from all columns and before reactivating the sampling operation from the first column, analog switch 22 is activated during period T, thus causing capacitor 25 to transfer its voltage to capacitor 26, which then holds the voltage from capacitor 25 during the period when the next sampling is being performed. The voltage held by capacitor 26 is then delivered to the column electrode (being a load) through the output buffer circuit comprised of gate-insulated transistor 27. The load can be considered to be that of capacitor 28 which synthesizes all the free capacitances of the column electrode.
Analog switches 23 and 24, respectively cause capacitors 26 and 28 to discharge their loads so that the voltage stored in both capacitors will not adversely affect the voltage to be discharged in the next step.
When performing a picture display using a liquid crystal display panel provided with the configuration described above, in order to correctly drive the liquid crystals using AC current, two-time scanning must be normally applied as a unit. AC current is then applied to the liquid crystals by inverting the polarity of the data signals fed to the column electrodes in each scanning period. As a result, when displaying TV pictures, if the aim is to display TV pictures using 525 scan lines (identical to those of a conventional NTSC-transmission format television set) only one-half (15 Hz) of the frame frequency is applied to the liquid crystals since the TV picture has a frame frequency of 30 Hz. Thus, a flicker is unavoidably generated on the displayed picture. To compensate for this, a jump scanning operation employed by conventional television sets is used and the polarity is widely inverted against each field so that 30 Hz of the AC current can be constantly supplied to the liquid crystals.
However, when performing liquid crystal display using the same number of scan lines as a conventional television set, a conventional method must be applied since each field receives video signals only through either odd or even numbered scan lines. For example, the frame memory is first activated. Then the picture signals corresponding to one-half the total number of scan lines is read from the frame memory before eventually being delivered to the column electrode drivers. Although the frame memory is needed as described above, when displaying TV pictures using a conventional TV display unit, which incorporates a matrix-type liquid crystal display panel via 525 scan lines (identical to a conventional NTSC television set) the provision of such a frame memory results in increased power consumption and more expensive operating cost.